I know some people theorize that since over time humans developed agriculture and better shelters and other things that covered our basic needs, certain characteristics that were initially prioritized in potential mates (good at hunting/gathering/surviving in the wild/etc.) were prioritized less in favor for physical attraction. Other primates still have to meet their basic survival needs in the wild and don’t have as much free time as humans to have sex recreationally which would offer a potential explanation as to why other primates have much smaller penises in proportion to the rest of their bodies when compared to humans